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Ultrastructural Effects in Zinnia Leaves of a Chlorosis-Inducing Toxin from Pseudomonas tagetis. Susanna M. Jutte, Department of Plant Pathology and Agricultural Research, U. S. Department of Agriculture, Department of Plant Pathology, University of Wisconsin, Madison, 53706; Richard D. Durbin, Department of Plant Pathology, and Agricultural Research, U.S. Department of Agriculture, Department of Plant Pathology, University of Wisconsin, Madison, 53706. Phytopathology 69:839-842. Accepted for publication 26 February 1979. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1979. DOI: 10.1094/Phyto-69-839.

A partially purified toxin from Pseudomonas tagetis caused chlorosis in developing zinnia leaves about 3 days after introduction of the toxin into the stem. Ultrastructurally the toxic effect was confined to the chloroplast. Only 1 day after treatment, chloroplast grana and stroma lamellae showed signs of disorganization, usually at the periphery of the plastid. After 2 days, this internal disorganization was severe, lipid globules were more numerous, and starch grains were greatly reduced in number and size. Short fibrils (presumably of DNA) and vesicles were evident. By 4 days, the chloroplast was scarcely recognizable. It was reduced in size and its outline was irregular, with invaginations that sometimes contained other organelles. The stroma lacked contrast because the ribosomes had disappeared and only remnants of the lamellae remained. In the more electronlucent stromal regions, the DNA fibrils had clumped and formed branched structures with fine tentacles. Lipid globules had increased in number and occurred in groups. No starch grains were present. The chloroplast envelope appeared to be intact.

Additional keywords: Zinnia elegans.